1. Field of the Invention
This invention relates to a communication transfer apparatus and a communication transfer method for transferring communications. More particularly, the present invention relates to a communication transfer apparatus and a communication transfer method for switching a terminal communicating with another terminal by way of the global IP (internet protocol) network to some other terminal belonging to the local IP network to which the first terminal belongs.
2. Related Background Art
As the development of Internet-related technologies, IP telephony that utilizes the Internet is becoming very popular. With IP telephony, a voice communication can proceed by means of RTP (real-time transport protocol) or some other protocol once a communication line is established by signaling by means of SIP (session initiation protocol), H.323 protocol or some other protocol.
Technological documents that describe the conventional art relating to the present invention include JP 11-205475 A, JP 2000-286882 A and JP 2003-46665 A.
However, the IP telephony that is becoming popular has a prerequisite that a single IP telephone terminal is connected to a single router that is installed in an office or a home.
In other words, when there is an IP telephone call, the router establishes a corresponding relationship between the combination of the global IP address and the global port number and the combination of the local IP address and the local port number of the called terminal by means of the technique of NAT (network address translation) or IP masquerade and the corresponding relationship continues as long as the IP telephone communication proceeds.
Therefore, if more than one IP telephone terminals are connected to the router, it may be conceivable to use either of the following two techniques in order to transfer the IP telephone communication of an IP telephone terminal to another IP telephone terminal.
The first one is to request the global network or the other end of the line to change the global port number that corresponds to the local IP address and the local port number of the IP telephone terminal before the transfer to the global port number that corresponds to the local IP address and the local port number of the IP telephone terminal of the destination of transfer.
However, any existing Internet service provider cannot accommodate such a request and any existing router cannot accommodate such a request either.
The second conceivable technique is to terminate the IP packets to be used with the other end of the line for IP telephone communication and install a particular device for IP telephone communications in the local IP network.
However, while an IP telephone communication can be realized between two terminals on a peer to peer basis, installing such a device for the purpose of termination and redistribution will again raise the cost that has been reduced once.
The above-identified problem arises not only in IP telephone communications but also in visual phone communications, television games and communications using messengers.